As a semiconductor integrated circuit or a flat panel display (FPD) has been more highly integrated, the wavelength of an exposure light in a photolithography process has become shorter. Thus, an ArF excimer laser beam (wavelength: 193 nm) having a wavelength shorter than an i-ray (wavelength: 356 nm) or a KrF excimer laser beam (wavelength: 248 nm) has been used. Accordingly, selected resists having a resolving power over the ArF excimer laser beam have been used. For example, see Japanese Patent Laid-open Publication Nos. 2004-182796, and 2005-037888.
A conventional KrF resist achieves an etching resistance by a benzene ring working as a terminal group (protecting group) in its chemical structure. Meanwhile, an ArF resist achieves an etching resistance by an adamantyl group instead of a benzene ring. This is because the benzene ring completely absorbs an ArF excimer laser beam (193 nm), thereby preventing a resist film from being exposed to light. See, for example, paragraph [0034] of Japanese Patent Laid-open Publication No. 2007-161987
However, there is a problem in that the etching resistance achieved by the adamantyl group is lower than that achieved by the benzene ring. For example, according to the investigation of the inventors of the present disclsoure, when etching speeds of both of ArF and KrF resist films were tested by using a mixed gas of CF4/O2 under the similar etching condition, the etching speed of the ArF resist film was about 300 nm/min, and the etching speed of the KrF resist film was about 260 nm/min. Since a higher etching rate can be achieved at a lower etching speed of a resist film, an ArF resist is required to have an increased etching resistance.